In a game arcade or a casino, there is installed a gaming machine, such as a slot machine, that provides a game to a user by rotating reels (also called drums) with different types of symbols displayed on surfaces of the reels. The reels are stopped after the rotation, and an award is paid to the player in accordance with the stopped symbols on a pay line.
In a gaming machine having reels, a stepping motor is often used as a drive motor for rotating the reel. Since the stepping motor rotates stepwise in response to an input pulse signal (command pulse), the frequency of the command pulse can be changed for changing the rotation speed of the stepping motor. In the gaming machine, using such a stepping motor, reel rotation control is performed in such a manner that the reel is rotated from a stop state and is stopped from a rotation state by changing the frequency or the period of the command pulse.
Generally, the command pulse given to the stepping motor to perform reel rotation control is generated in interrupt service executed by a microcomputer provided in the gaming machine every predetermined time T (for example, 1 ms (millisecond)). For example, to generate a command pulse in pulse period 5T (for example, 5 ms) at the low-speed rotation time just after rotation starts, an interrupt service program is designed for outputting one pulse each time five interrupt services are executed; on the other hand, to generate a command pulse in a cycle T (for example, 1 ms) at the high-speed rotation time, the interrupt service program is designed for outputting one pulse each time one interrupt service is executed. That is, such a gaming machine controls the rotation speed of the stepping motor for rotating the reel under the control of the software program.
Incidentally, when a load torque exceeding a through torque characteristic (also called continuous characteristic, pull-out torque characteristic) is applied for some reason while the stepping motor is rotating, there is caused a phenomenon called step-out in which the stepping motor becomes impossible to rotate following to the command pulse. Particularly, at a high-speed rotation, high-frequency current becomes hard to flow into a coil of the stepping motor and therefore reduction in the motor torque is remarked and step-out becomes easy to occur.
If such step-out is about to occur, the frequency of the command pulse is lowered (the period can be extended) for circumventing such trouble. However, if the rotation speed is controlled by software as described above, the control is limited to the execution interval T of the periodic interrupt process and thus the command pulse cannot be generated based on intermediate step period (“step period” equivalent to “frequency”) like 1.5T although the pulse period can be changed to an integral multiple (for example, from T to 2T, 3T, etc.,). Thus, to lower the pulse frequency to prevent step-out, the pulse frequency is largely lowered, for example, from pulse frequency 1/T (=1000 Hz) to ½T (=500 Hz) and the rotation speed drastically reduces. Accordingly, it becomes difficult to perform proper rotation control of the stepping motor.